The present invention relates to pipes suitable for pneumatic transportation, or the like. The material to be transported may be mainly a liquid such as water, oil, liquid chemicals, or the like, a gaseous body such as air, gas, or the like, agricultural products such as grain, corn, or the like, or waste materials in a factory, or the like. The present invention relates particularly to pipes which have superior pressure-withstanding properties and which are suitable for the transportation of a liquid, gaseous body, grain, or the like, which produces a high pressure in the pipes. The present invention also relates to a method for manufacturing such pipes.
Conventionally, a pressure-withstanding pipe has a pipe wall with a main portion thereof made of a soft synthetic resin material. In addition, reinforcing filaments made of a hard synthetic resin material or reinforcing wires made of metal are helically embedded in the pipe wall as a reinforcing body. Such a pipe is known and manufactured. Further, a pipe of this kind having a large number of natural fiber filaments, metal wires, or the like, further embedded and arranged in parallel to each other and disposed all over the circumferential surface of the pipe wall is also known.
A pipe in which a fiber reinforcing belt is embedded in the pipe wall by using cloth in place of the fiber filaments or wires in the pipe mentioned directly above also is known.
Further, it is possible to consider a method of manufacturing a pipe (OA) in which a fiber reinforcing belt is embedded in the pipe wall in addition to such reinforcing filaments as shown in FIG. 19, for example. In this method, a belt body (01a), which is made of a soft synthetic resin material and in which hard synthetic resin reinforcing filaments (02) are embedded, is extruded from a synthetic resin extruder and helically wound, with adjacent windings being joined by fusing adjacent edge portions with each other; then a fiber cloth reinforcing belt (03) is helically wound on the outer circumferential surface of the belt body (01a) at the same pitch as that of the belt body (01a) while partially overlapping or abutting adjacent edge portions of the reinforcing belt (03); and then a soft synthetic resin flat belt body (01b) formed by being extruded by another synthetic resin extruder is helically wound on the outer surface of the reinforcing belt (03) at the same pitch as that of the belt body 01a. Again, as the belt body (01b) is wound, the end portions of adjacent windings are joined with each other by fusing.
In the case of employing such a method, however, complicated mechanical equipment is required as there are three winding operations. In addition, the produced pipe (OA) is disadvantageous in that the position where the soft reinforcing filaments (02) are embedded becomes thick and it is difficult for the embedded fiber reinforcing belt (03) to be firmly maintained in the pipe wall, particularly at the overlapped portion (or the abutted portion) of the side edge portions thereof. Therefore, the embedding state of the belt (03) is apt to become unstable. Further, particularly in the case where the pipe is used for transporting a liquid or the like providing a high pressure in the pipe, the overlapped portion (or the abutted portion) located between the inner and outer soft belt bodies (01a) and (01b) is apt to cause a peeling phenomenon between the belt bodies. This peeling phenomenon is due to an expansion action exerted in the circumferential or radial direction of the pipe and an extension action exerted in the longitudinal or axial direction of the pipe due to pressure exerted on the pipe by the transported material in a radial and an axial direction, respectively. The peeling phenomenon can also be caused by tensile stresses which may be created when the pipe is placed in a curved state. In addition, the overlapping portion of the fiber reinforcing belt (03) is apt to slide upon generation of the extension action of the pipe so as to prevent the extension phenomenon of the pipe.